1. Field of the Invention
The present invention relates to a system for etching polysilicon in fabricating a semiconductor device and, more particularly, to a system for etching polysilicon in fabricating a semiconductor device which can prevent contamination of a wafer with polymers formed during a polysilicon etching process in which the polysilicon coated on the wafer is selectively etched.
2. Discussion of the Related Art
In a polysilicon etching process, polymers are reaction products formed by the reaction of plasma and polysilicon when a photoresist film is coated on a polysilicon film formed on a wafer and exposed.
Referring to FIG. 1, a conventional device for etching polysilicon in a semiconductor fabricating process includes a reaction chamber 3 having a wafer chuck 2 placed therein onto which a wafer 1 is loaded for etching. A passage 11 is connected to the reaction chamber 3 for discharging a reaction gas from the chamber. A vacuum pump 7 is disposed on one side of the passage 11 for evacuating the reaction chamber 3. A pressure control valve 4 disposed at an inlet to the vacuum pump 7 controls the flow rate of the gas being pumped, and a valve driving motor 6 drives the pressure control valve 4.
In the conventional device for etching polysilicon using the aforementioned system, the process includes maintaining a pressure in the reaction chamber 3 at a predetermined pressure of 5.about.7 Torr by driving the vacuum pump 7 while injecting a reaction gas into the reaction chamber 3 after a wafer 1 is loaded on the wafer chuck 2, which is an anode.
However, use of the conventional device as shown in FIG. 1 for etching polysilicon results in accumulation of polymers, which are reaction products of plasma and polysilicon, on the surface of the pressure control valve 4 and inside of the vacuum pump 7. Particularly, a significant amount of polymers forms on the reaction chamber side surface of the pressure control valve 4 due to its mounting position. After finishing the etching process, the vacuum pump 7 continuously pumps for a predetermined time period for discharging the polymers from the reaction chamber 3 to outside of the device. Since no reaction gas is injected into the chamber during that time period the pressure inside of the reaction chamber 3 drops sharply to 0 mm Torr. Consequently, the conventional device for etching polymers has an inherent problem in that the polymers act as foreign matter in the etching process. Polymers re-enter the reaction chamber 3 from vibration of the pressure valve 4 caused by the sharp drop of pressure within the chamber. Further, the vibration loosens the polymers deposited on the inlet of the vacuum pump 7 and pressure control valve 4 which causes the floating polymers to re-enter the reaction chamber 3.
Because the bottom opening of the vacuum pump 7, is located above the opening to the reaction chamber 3, the conventional device for etching polysilicon allows a significant amount of polymers deposited inside of the vacuum pump to migrate through the opened inlet of the vacuum pump 7. When the vacuum pump 7 is suddenly stopped, the polymers deposited on the pressure control valve 4 (and in the pump 7) drop down during opening/closing of the pressure control valve 4 which seriously contaminates the reaction chamber 3.